Resonant tank is employed as a basic converting unit in resonant converters. When resonance occurs, current or voltage of the resonant tank periodically crosses zero. This allows transistors in the resonant converter to turn on or turn off at zero voltage or zero current condition, so as to reduce switching loss of the resonant converter.
To realize high power factor, resonant converters typically adopt two-stage structure as shown in FIG. 1, wherein a dedicated power factor correction (PFC) circuit is utilized. However, the PFC circuit used as the first stage not only increases cost, but also harms power density and efficiency of the resonant converter.